Abstract: A method and apparatus are provided for forming insulated cable from uninsulated cable. Uninsulated cable is fed from a source to a guiding mandrel, and molten cable insulation is extruded between a guider tip and forming die to coat with insulation the cable passing through the mandrel. The coated cable is continuously withdrawn from the forming die. In order to prevent damage to the guider tip, the cross-sectional dimensions of the uninsulated cable are sensed during feeding to the guiding mandrel, and an electrical signal is generated in response to the cable sensing if any cross-sectional dimension of the cable is greater than a predetermined amount. The operation is shut down and/or an alarm is activated in response to the generated electrical signal. Sensing is accomplished utilizing a sensing member mounted for slidable movement against a spring bias, and having a conically shaped aperture formed therein and tapering in the direction of movement of the cable through the aperture.